Metal Organic Framework Crystals in Mixed-Matrix Membranes: Impact of the Filler Morphology on the Gas Separation Performance.

Mixed-matrix membranes (MMMs) comprising NH-MIL-53(Al) and Matrimid or 6FDA-DAM have been investigated. The MOF loading has been varied between 5 and 20 wt%, while NH-MIL-53(Al) with three different morphologies: nanoparticles, nanorods and microneedles have been dispersed in Matrimid. The synthesized membranes have been tested in the separation of CO from CH in an equimolar mixture. At 3 bar and 298 K for 8 wt% MOF loading, incorporation of NH-MIL-53(Al) nanoparticles leads to the largest improvement compared to nanorods and microneedles. The incorporation of the best performing filler, NH-MIL-53(Al) nanoparticles, to the highly permeable 6FDA-DAM has a larger effect, and the CO permeability increased up to 85 % with slightly lower selectivities for 20 wt% MOF loading. Specifically, these membranes have a permeability of 660 Barrer with CO/CH separation factor of 28, leading to a performance very close to the Robeson limit of 2008. Furthermore, a new non-destructive technique based on Raman spectroscopy mapping is introduced to assess the homogeneity of the filler dispersion in the polymer matrix. The MOF contribution can be calculated by modelling the spectra. The determined homogeneity of the MOF filler distribution in the polymer is confirmed by FIB-SEM analysis.